Chapter 6: Bone Tissue and the Skeletal System

6.1 The Functions of the Skeletal System

• Support: Framework for the body, maintains posture.

• Movement: Acts as levers for muscles.

• Protection: Shields vital organs (e.g., skull protects the brain).

• Mineral and Fat Storage: Stores minerals (calcium, phosphate) and fat in yellow marrow.

• Hematopoiesis: Red bone marrow produces blood cells.

• Hormonal Role: Produces osteocalcin for insulin regulation and glucose homeostasis.

6.2 Bone Classification

• Long Bones: Longer than wide (e.g., femur); levers for movement.

• Short Bones: Cube-shaped (e.g., carpals); provide stability.

• Flat Bones: Thin, curved (e.g., skull); protect organs and provide muscle attachment.

• Irregular Bones: Complex shapes (e.g., vertebrae); protect and support.

• Sesamoid Bones: Small round bones in tendons (e.g., patella); reduce friction.

6.3 Bone Structure

• Macroscopic Structure:

  • Diaphysis: Shaft of long bone.

  • Epiphysis: Ends containing spongy bone.

  • Metaphysis: Contains growth plate in growing bones.

  • Medullary Cavity: Hollow space with yellow marrow.

  • Endosteum: Lining of medullary cavity; involved in remodeling.

  • Periosteum: Outer covering providing blood supply and tendon attachment.

• Microscopic Structure:

  • Compact Bone: Dense, contains osteons housing blood vessels.

  • Spongy Bone: Porous, supports red bone marrow.

• Bone Cells:

  • Osteogenic Cells: Stem cells forming osteoblasts.

  • Osteoblasts: Build bone matrix.

  • Osteocytes: Maintain bone tissue.

  • Osteoclasts: Resorb bone matrix.

6.4 Bone Formation and Development (Ossification)

• Intramembranous Ossification: Direct bone formation from mesenchymal tissue (e.g., skull).

• Endochondral Ossification: Replacement of cartilage with bone.

• Bone Growth:

  • Longitudinal: Grows at the epiphyseal plate with zones: resting, proliferation, hypertrophic, and calcification.

  • Appositional Growth: Increases bone diameter.

6.5 Fractures and Bone Repair

• Types of Fractures:

  • Closed: Bone breaks without skin pierce.

  • Open: Bone breaks and pierces skin.

  • Various other types: transverse, spiral, comminuted, impacted, greenstick.

• Stages of Repair:

  • Hematoma Formation: Blood clot at fracture site.

  • Callus Formation: Stabilizes break with cartilage.

  • Bony Callus Formation: New bone formed by osteoblasts.

  • Bone Remodeling: Restoration of original structure.

6.6 Exercise, Nutrition, and Hormones Affecting Bone Health

• Exercise: Weight-bearing activities stimulate remodeling and density.

• Nutrition: Key nutrients include calcium, vitamin D, K, magnesium, and omega-3 fatty acids for bone strength.

• Hormones: Regulate growth, metabolism, and calcium levels (e.g., growth hormone, sex hormones, calcitonin).

6.7 Aging and Bone Tissue

• Effects of Aging: Decreased bone mass, increased fracture risk, reduced collagen production.

• Osteoporosis Prevention: Adequate intake of calcium and vitamin D, regular exercise, and hormonal therapy when severe.

Summary of Key Concepts

The skeletal system provides support, movement, protection, storage, and blood cell production. Bone tissue consists of osteocytes, osteoblasts, and osteoclasts involved in remodeling. Ossification occurs through intramembranous and endochondral methods. Healing of fractures follows a specific process, significantly influenced by exercise, diet, and hormonal health. Aging leads to bone density loss and raises osteoporosis risk.

Chapter 7: The Axial Skeleton

7.1 Divisions of the Skeletal System

• Axial Skeleton: 80 bones (skull, vertebral column, thoracic cage).

• Appendicular Skeleton: 126 bones (limbs, girdles).

7.2 The Skull

• Total Bones: 22 bones; cranial and facial bones.

• Cranial Bones: 8 (frontal, parietal, temporal, occipital, sphenoid, ethmoid).

• Facial Bones: 14 (maxillae, palatine, zygomatic, nasal, lacrimal, inferior nasal conchae, vomer, mandible).

• Features: Sutures, paranasal sinuses, hyoid bone.

7.3 The Vertebral Column

• Total Bones: 26 vertebrae supporting the body, protecting the spinal cord.

• Regions: Cervical (7), thoracic (12), lumbar (5), sacral (5 fused), coccygeal (4 fused).

• Features: Intervertebral discs with nucleus pulposus and annulus fibrosus.

7.4 The Thoracic Cage

• Protects: Heart, lungs, major vessels.

• Sternum: Manubrium, body, xiphoid process.

• Ribs: True (1-7), false (8-12), floating (11-12).

7.5 Embryonic Development of the Axial Skeleton

• Development: From mesoderm; involves notochord formation and ossification events.

• Congenital Abnormalities: Cleft palate, spina bifida.

Key Takeaways

Axial skeleton comprises the skull, vertebral column, and thoracic cage, crucial for protection and movement. Each bone plays vital roles. Vertebral column includes specialized vertebrae; the thoracic cage offers organ protection, developed from mesoderm.